INSECTICIDES 481 



ceiver, roll sulfur is formed. Flour of sulfur is made by grind- 

 ing roll sulfur to a fine powder. 



In the form of a powder or dust, sulfur is especially valuable 

 against red spider. In California flowers of sulfur mixed with 

 equal parts of hydrated lime is blown on the trees for the control 

 of red spider and mite. Sulfur is sometimes used for the same 

 purpose mixed with water at the rate of 1 pound in 3 gallons of 

 water, in which a little soap has been dissolved to help keep the 

 sulfur in suspension. The sulfur settles quickly and should be 

 agitated constantly during spraying. The sulfur will remain in 

 suspension longer if first made into a paste with water contain- 

 ing i of 1 per cent of glue. 



Lime-sulfur Solution 



A solution of lime and sulfur was first used as an insecticide 

 in California in 1886. The mixture at that time was known 

 as the lime-sulfur and salt wash, but experience has shown that 

 the presence of the salt does not increase the value of the wash, 

 and it is now usually omitted. The lime-sulfur solution is the 

 most widely used, safest and most efficient contact insecticide 

 now available for the control of scale insects and blister-mite. 



In many regions it has also replaced Bordeaux mixture for 

 the control of fungous diseases on apple and pear. 



When lime and sulfur are boiled together in water, a compli- 

 cated chemical reaction takes place. The calcium (Ca) con- 

 tained in the lime (CaO) combines with the sulfur (S) in varying 

 amounts. Two of the compounds thus formed are calcium 

 pentasulfid (CaSs) and calcium tetrasulfid (CaS4), containing 

 respectively 80 and 76 per cent of sulfur. At the same time 

 there is always formed a smaller quantity of thiosulf ate (CaS203) . 

 These three compounds are soluble in water and give to the solu- 

 tion its insecticidal value. It is supposed that a solution will be 

 more effective in proportion as it contains a higher percentage 



